Deinking system for carbonate pulping

ABSTRACT

A process for deinking paper being recycled in a carbonate pulping procedure which is performed in the absence of hydroxides and peroxides is improved by the addition of (a) a non-ionic surfactant deinking agent having a cloud point of about 55 to 85, preferably 60-70, and (b) at least two different fatty acid ink collectors: (i) a C16 to C20 fatty acid and (ii) a C22 to C30 fatty acid, the ink collectors being used in a weight ratio of from about 98:2 to 70:30.

This application claims the benefit under 35 U.S.C. §119(e) of prior U.S. Provisional Patent Application No. 60/526,359 filed Dec. 1, 2003, which is incorporated in its entirety by reference herein.

BACKGROUND OF THE INVENTION

Deinking of recycled paper products is becoming more and more important to deal with the substantial increase in paper recycling that is occurring. Such systems have been reasonably highly developed for highly alkaline sodium hydroxide/peroxide pulping systems, but little attention has been paid to deinking systems for use in neutral or near-neutral carbonate pulping operations.

Exclusive of mechanical aspects, conventional highly alkaline peroxide paper pulping processes which incorporate flotation deinking procedures can be divided into three distinct chemical regimes: pulper, floatation, and bleaching. A typical sodium hydroxide/hydrogen peroxide pulping regime operates at high pulper pH, e.g. about 8.5-11.0, and requires two separate bleaching stages to achieve the desired effect. Stage 1 bleaching takes place in the pulper and helps to offset alkali yellowing of the fiber before a floatation procedure removes ink from the system. Stage 2 bleaching is performed after the flotation procedure, but before the deinked pulp moves forward to a paper machine. The bleaching agents in stages 1 and 2 can be the same or different. These types of pulping operations are conducted in the presence of hydrogen peroxide, sodium hydroxide, sodium silicate, a chelant, and sometimes other chemicals and are intended to achieve a desired stage 1 brightness and ink release from the recycled fibers.

The present invention, however, is directed to deinking of sodium carbonate pulping systems which operate at near-neutral pulper pH, i.e. about 7.2 to 8.5, preferably about 7.5 to 8.0, and require only a single bleaching procedure (after flotation) to achieve the desired brightness effect. No sodium hydroxide, hydrogen peroxide or chelant are used during pulping. Deinking with carbonate pulping systems is disclosed in U.S. Pat. No. 5,882,476, the subject matter of which is incorporated herein by reference, of Solvay Minerals, Inc. The patent discloses the addition of a surfactant to the system. The only specific surfactant disclosed is DI-600 from Kao Japan. DI-600 is a difficult to classify mixture prepared by a manufacturing process in which tallow is broken down forming glycerin, half esters, and acids, etc. all of which are subsequently alkoxylated. The resulting surfactant composition has a cloud point of 45-48° C. With the increasing demands placed upon deinking of recycled paper with the vast increase in recycling of paper products as well as current ink chemistry, i.e. the increasing use of flexographic inks, the Solvay technology even with a surfactant having this low a cloud point this has not worked sufficiently.

Deinking systems have been successfully developed for the more common sodium hydroxide pulping systems. However, the mere substitution of those deinking systems into carbonate pulping regimes has not been successful.

Zero and/or low sodium hydroxide content carbonate pulping systems are desirable because they favor suppression of both dispersion effects and the formation of “stickies” which form in pulp due to alkaline hydrolysis. The carbonate pulping systems avoid the need for peroxide bleaching (an exothermic reaction) in the pulper, and thereby allow a mill to use lower operating temperatures during deinking. The lower temperature system also helps in the suppression of stickies. Other advantages of neutral or near neutral deinking are known to the art and thus not repeated here.

U.S. Pat. No. 5,288,369 (Ishibashi et al) discloses the advantages of fatty acid enrichment during ink removal in a standard sodium hydroxide/peroxide pulping system. It does not disclose carbonate pulping systems as are used in the present invention.

Other patents which disclose deinking of highly alkaline pulping systems, i.e. in the presence of sodium hydroxide, hydrogen peroxide, etc., include: U.S. Pat. Nos. 6,013,157; 5,840,157; 5,837,097; 5,718,801; 5,417,808; 4,780,179; and 4,390,395. All identified patents are incorporated herein by reference.

The prior art contains no recognition that in a carbonate pulping system of the present invention, unlike the sodium hydroxide/peroxide prior art systems, (i) there is an advantage to using high cloud point surfactants of improved detergency as the deinking agent and (ii) there is a need for rapid ink capture requiring the presence of a mixture of at least two fatty acid ink collectors. Moreover, it has unexpectedly been found that the enhanced ink collection system of the present invention reduces bleach demand and sheet dulling.

SUMMARY OF THE PRESENT INVENTION

The present invention is directed to a process of deinking paper being recycled by a carbonate pulping procedure that is performed in the absence of hydroxides and peroxides. The process entails pulping the paper in the presence of sodium carbonate (generally in combination with a minor amount of sodium silicate) in combination with a non-ionic, alkoxylated alcohol surfactant deinking agent having a cloud point of about 55 to about 85° C., preferably about 60 to about 70° C., and further in combination with two different ink collectors: the first being a C16 to C20 fatty acid or a mixture of such acids, and the second being a C22 to C30 fatty acid or a mixture of such acids, the two ink collectors being used in a weight ratio of from about 98:2 to 70:30, preferably about 90:10. The fatty acid ink collectors are normally fully hydrogenated (saturated), though for overall economic purposes up to about 25% by weight of the saturated fatty acid ink collectors may be substituted by one or more unsaturated fatty acids, particularly a mixture thereof such as tall oil fatty acids (TOFA).

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a graph of the Delta Brightness of ink collection systems evaluated in Example 2, including systems of the prior art (NaStearate, NaTallate), of the present invention (KStearate/KBehenate 9/1), and a comparison to the present invention (KStearate/KBehenate 4/1) versus time.

FIG. 2 is a graph of ERIC Number Reduction of the results of Example 2.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The deinking of paper being recycled is performed by a carbonate pulping procedure in the substantial absence of hydroxides and peroxides. The process entails pulping of paper in the presence of sodium carbonate, sodium silicate, and optionally sodium sulfite, in combination with (a) a non-ionic, alkoxylated alcohol surfactant deinking agent having a cloud point of about 55 to about 85° C., preferably about 60 to about 70° C., most preferably about 65 to 68° C., and further in combination with (b) two different ink collectors—one being a C16 to C20 fatty acid or a mixture thereof, and the other being a C22 to C30 fatty acid or a mixture thereof, the two ink collectors being used in a weight ratio of from about 98:2 to 70:30. The fatty acid ink collectors are preferably saturated (fully hydrogenated). For overall economic purposes, the saturated fatty acid ink collectors may be extended by up to about 25% by weight of one or more unsaturated fatty acids, e.g. a mixture such as tall oil fatty acids (TOFA).

Suitable surfactants for use as deinking agents are non-ionic C14 to C24 alcohol alkoxylates that have a cloud point of about 55 to 85° C., preferably about 60 to 70° C., most preferably about 65 to 68° C. While a mixture of alcohols, such as a C14-C16 blend or a C16-C18 blend, can be alkoxylated to form the surfactant, better performance has been found when a substantially pure alcohol feedstock, such as C16 or C18, is used. On both a performance basis and a cost-performance basis a pure C18 alcohol feedstock is most preferred. The surfactant is generally used at a rate of about 1 to 10, preferably about 2 to 6, pounds per ton of paper. This corresponds to a rate of about 0.05 to 0.5, preferably about 0.1 to 0.3,% by weight of the paper being processed.

The other critical component of the present invention is the ink collector system. Two different fatty acid ink collectors are used. The first is a C16 to C20 fatty acid or a mixture of such fatty acids. The second is a C22 to C30 fatty acid or a mixture of such fatty acids. The ink collectors are used in a weight ratio of from about 98:2 to 70:30. The fatty acid ink collectors are preferably fully hydrogenated (saturated). For economic purposes, up to 25% by weight of the combined saturated fatty acid ink collectors may be replaced by one or more unsaturated fatty acids. A mixture of unsaturated predominantly C16 and C18 fatty acids such as tall oil fatty acids (TOFA) is a suitable extender.

The fatty acid ink collectors are used in total amounts ranging from about 1 to 15 pounds per ton dry paper. Preferably about 2 to 10 pounds per ton are used. Most preferably about 4 to 6 pounds per ton are used.

The chemicals normally present in a paper recycle system of the present invention using a carbonate pulping regime vs. those of a typical caustic pulping system (including the first bleaching stage) can be compared as follows: PULPER/FLOTATION Typical Caustic Inventive INGREDIENTS pulping/bleaching Carbonate Sodium Hydroxide yes no Sodium Silicate yes yes Sodium Carbonate no yes Sodium Sulfite Optional Optional Ink Collectors (fatty acids) yes yes Deinking agent (surfactant) yes yes Biocide Optional no Chelant yes no pH Pulper 8.8-10.5 7.2-8.5 pH Floatation 8.0-9.0 7.0-8.0

After a flotation step, both systems require a post-pulping bleaching operation in which the following chemicals are used: POST-PULPING BLEACHING Hydrogen Peroxide yes no Sodium Hydrosulfite Optional yes Biocide Optional no Chelant yes Optional

Normally all of the pulper and deinking chemicals are added into the pulper, though portions of the fatty acids and/or surfactant can be added by split addition, i.e. divided between the pulper and the feed to the flotation cell, as this may enhance ink capture. The sodium silicate and sodium carbonate are generally used at a ratio between about 95 to 5 and about 50 to 50 by weight with respect to each other. More preferably the sodium carbonate is used at a rate of about 2 to 20, preferably about 5 to 10, pounds per ton. The sodium silicate is used at a rate of about 10 to 30, preferably about 12.5 to 25, and most preferably about 15 to 20, pounds per ton. Sodium sulfite may also be added. When used it is added at a rate of about 2 to 8 pounds per ton.

Although biocides are not needed in carbonate pulping systems, they may be added for simple microbial control if desired.

In a conventional alkaline sodium hydroxide pulping process, chelants are necessary to help control transition metals in the stock that cause catalytic peroxide decomposition. Chelants are not required in the carbonate pulping systems of this invention, but can be used if so desired to increase the bleach response during post-pulping bleaching.

Standard TAPPI test procedures were used for ERIC and brightness measurements in order to track deinking performance. Hyper-washing tests were run in order to assess the initial ink release during pulping.

Hyper-washing tests were run in order to assess the initial ink release during pulping, i.e., to assess if all available ink has been released from the fiber. This test is done usually after pulping, although it can be done at other times throughout the process whenever one wants to quantify the amount of free ink in the system. The hyper-washing test is conducted using a Britt filtration jar (approximately 1 liter capacity) whereby 10 g oven-dried pulped stock (furnish obtained after pulping) is washed with 5 liters of deionized (DI) water. The stock is placed in the Britt jar, diluted with wash water, and the agitation is turned on to about 1600 rpm. The stock is stirred in this manner for one minute, and then the jar allowed to drain with the agitation still on. When the level approaches the agitator, the drain is closed and the cell refilled with DI wash water for another minute wash with agitation. The process is repeated until all 5 liters of DI wash water have been consumed. The stock is then filtered and made into a pad for ERIC and brightness measurements. The test has a repeatability of ±10 to 15 ppm ERIC within a test series.

Mill performance data clearly shows that the carbonate based deinking system gives satisfactory ink release during pulping and that the ink release is equivalent to that achieved using sodium hydroxide-based pulping regimes. This was true for Ponderay, Alabama River News Print, and Augusta News Print using Voith, Black Clawson and PDM deinking equipment respectively. The ink release was not influenced by equipment design.

The following non-limiting examples are provided to demonstrate the efficacy of the present invention. All parts and percents are by weight unless otherwise specified.

EXAMPLES Example 1

The criticality of surfactant and fatty acids to a successful deinking process for a carbonate pulping operation can be seen in the following comparison of two commercial plant trials, one a success and one a failure because it did not produce any improvement in deinking. The chemical additives used and the deinking results are shown below in Tables 1 and 2. TABLE 1 Successful Trial Base- Inven- Unsuccessful Trial line tion Baseline Failure Sodium Hydroxide 0.80 — 0.80-1.05 — Sodium Silicate 0.60 0.62 0.60-0.80    0.25-2.00 Sodium Carbonate — 0.30 —    0.05-1.00 Sodium Sulfite — 0.10 —   0.125-1.95 Hydrogen Peroxide 0.90 — 0.90 — Chelant 0.20 0.20 0.20 — Fatty acid salts 0.04 0.30 0.04    0.04-0.053 Surfactant, 0.16 — 0.12-0.16    0.05-0.25 Cloud point 46-50° C. Cloud point 66-68° C. — 0.03 — — Sodium Hydrosulfite 0.15 0.15 0.15 0.15

TABLE 2 Successful Trial Unsuccessful Trial Baseline Invention Baseline Failure Brightness Gain (ISO) 15.0 15.2 15.6 12.8 % Efficiency 76.8 80.5 75.2 67.3 (Ink Removal) Hyper-wash Brightness 52.9 54.2 52.5 52.2 Hyper-wash ERIC 235 212 251 260

During the failure, the hyper-wash data ex-pulper clearly showed that all available ink had been released during pulping. During flotation ink removal, however, efficiency and brightness gain fell during the course of the trial. The collector package used had been designed for a conventional caustic pulping regime and thus utilized a low cloud-point surfactant, i.e. one having a cloud point of about 46-50° C. with <20% tall oil fatty acid (TOFA) mixture present. This combination was ineffective during flotation of a carbonate pulped furnish. Thus it was discovered that the problem was not one of initial ink release from the recycled fibers, but rather one of ink removal efficiency during flotation.

During the successful trial, the mill hyper-wash data ex-pulper clearly shows that all available ink has been released from the fiber during pulping. Ink removal efficiencies during flotation were acceptable. Brightness gains, ERIC and fiber yield values remained on target for the complete trial. Dispersion effects were minimized/controlled. The collector package (fatty acids and surfactant) was effectively married to the carbonate pulping regime by controlling the fatty acid composition as well as increasing the surfactant cloud point to 66-68° C. The replacement of 10% of the stearic acid (C18) with behenic acid (C22) gave the desired fast ink capture early in the process, minimizing any significant ink build up in the system. This facilitated continuous running.

The above fatty acid enrichment also allowed the use of higher cloud point surfactants that gave improved detergency as well as the desired foam volume i.e. for effective ink transport out of the float cell without causing dispersion. In a conventional sodium hydroxide pulping system, higher cloud point surfactants having higher detergency are unacceptable because they are dispersive of the released ink particles.

Example 2

Laboratory testing of various systems was performed to compare a number of variables—fatty acids both individual and in combinations at varying levels. The testing was conducted using a Voith, 30 liter lab cell because it had previously been found to have a good correlation to actual mill performance. All mill materials, like furnish, mill water and mill chemicals were used to benchmark the cell against actual plant performance. Further optimization studies were conducted in both the lab and mill environment using this benchmark as a reference point.

The results of varying the fatty acids are shown in FIGS. 1 and 2. The fatty acid screening runs were conducted at low surfactant doses i.e., <10.00% of the total combined FA/surfactant dose. The surfactant was used essentially as a hydrotrope to generate reliable data (at the same level of rejects) with no rejects/foam surging due to furnish changes. The results show a substantial advantage of hydrogenated/hard fatty acids (low iodine values <10) as compared to TOFA (iodine value about 140) with respect to ink capture. The behenic acid blends with stearic acid show optimum performance at a 10/90 ratio of behenic acid/stearic acid respectively over all other combinations. Higher behenic ratios (40/60) show no improvement over the lower ratios and are substantially equivalent to stearic acid alone.

It is noted that the actual fatty acid deinking agent (DIA) is the calcium salt of the fatty acids, made in-situ by the simple sodium or potassium/calcium exchange of the pre-neutralized fatty acid. Calcium water hardness is required to effectively complete this exchange. Most calcium salts are hydrophobic and have extremely low water solubility i.e. they readily accumulate at the air-water interface where ink collection takes place. The system was effective at a 50.0 ppm lower limit of calcium. Higher levels of calcium (>100 ppm) did not significantly improve the response. The fatty acids were pre-neutralized before use using sodium hydroxide, potassium hydroxide, or ammonium hydroxide in a conventional manner.

The superior 10/90 behenic acid/stearic acid ratio was then paired with a range of surfactants of varying cloud points to further optimize the process.

Higher cloud point surfactants are favored since they can accommodate significant temperature swings that occur during processing without insolubilizing the surfactant. They also provide the most reliable foam pad during flotation which is tolerant of significant furnish and temperature changes. Most furnishes tested were a mixture of ONP/OMG. Any loss in quality and/or quantity of OMG will adversely affect foam. With the higher cloud point surfactants, the float cells maintained a continuous surface foam without balding and/or collapsing before the foam pad (which is ink carrying) reached the rejects trough. This effect was validated in the successful trial. While the higher cloud point surfactant would be expected to exhibit higher dispersive properties, use of the behenic acid/stearic acid blends avoided the potential problem. TABLE 3 SURFACTANT SCREEN FA/Surfactant Cloud Point Brightness ERIC Efficiency % Dosage ° C. TAPPI ppm % 0.6/0.06 80-82 51.6 240 75.0 0.6/0.06 62-64 51.4 256 73.6 0.6/0.06 46-48 49.0 404 63.9 0.6/0.06 29-31 48.0 350 65.0 Surfactant only 0.2 80-82 48.7 380 68.2 0.2 62-64 49.1 322 68.2 0.2 29-31 49.1 352 65.7

The “fatty acid” used during these tests was the preferred 10/90 w/w mixture of behenic acid/stearic acid, sodium or potassium salt. The potassium salts are favored due to enhanced solubility in mill water. Each of the 4 different cloud point surfactants was an ethylene oxide/propylene oxide (EO/PO) alkoxylate on a C18 stearyl alcohol base, with varying ratios of EO to PO. Higher amounts of surfactant can be used in combination with the fatty acid up to a 1:1 ratio with no appreciable change in performance. In the interests of cost performance, surfactant use is minimized.

Example 3

Hyper-wash testing was performed at multiple commercial mills to compare the benefits of the present invention (carbonate pulping plus deinking technology) vs. conventional sodium hydroxide technology. The results are shown below in Table 4 in which “Ponderay” is Ponderay Newsprint of Washington, “ARN” is Alabama River Newsprint, of Alabama, and “Augusta” is Augusta Newsprint of Georgia. TABLE 4 PULPER RESPONSE ONP/OMG Brightness, ERIC Mill Ratio Hydroxide Carbonate % ISO ppm Ponderay 80/20 yes no 51.0 270 Ponderay 80/20 no yes 49.5 270 ARN 95/5  yes no 52.4 260 ARN 95/5  no yes 51.0 240 Augusta 80/20 yes no 50.5 168 Augusta 80/20 no yes 53.2 178

Example 4 Bleaching Response of Invention vs. Alkaline Peroxide Chemistry

Mill performance data also shows that sodium hydrosulfite bleaching alone is sufficient to attain target brightness using the carbonate-based deinking system of the present invention, which confirms the superior bleach response of the pulp processed using the carbonate system. The results are shown in Table 5 in which “Caustic” refers to a standard sodium hydroxide deinking system and “Invention” to a system in accordance with the present invention. TABLE 5 Sodium ONP/ Hydrogen Hydro- OMG Peroxide, sulfite, Brite ERIC, Caustic or Mill ratio % % ISO ppm Invention Ponderay 80/20 1.00 0.3 52.0 275 Caustic Ponderay 80/20 — 0.3 52.7 231 Invention ARN 95/5  0.60 0.25 51.9 272 Caustic ARN 95/5  — 0.25 51.5 262 Invention Augusta 80/20 0.40 0.2 50.5 168 Caustic Augusta 80/20 — 0.2 53.2 178 Invention

Conventional, alkaline-peroxide deinked stock has a low response to sodium hydrosulfite post-bleaching (after flotation and thickening). The deinked stock of this invention has an unexpectedly greater response to sodium hydrosulfite post-bleaching (after flotation and thickening).

Sodium hydrosulfite is commonly used to bleach pulp (both virgin and recycled) for newsprint. In comparing the bleaching response of the carbon-ate deinked pulp (one-stage) of this invention vs. conventional alkaline-peroxide deinked pulp (two-stage), the following conclusions were reached: (i) at low application levels of hydrosulfite (<5 lb./ton or 0.25%), the carbon-ate deinked stock has about the same bleach response as conventionally deinked stock; and (ii) at higher application levels of hydrosulfite (>5 lb./ton or 0.25%), the carbonate deinked stock had a greater response to the hydro-sulfite bleach than conventionally deinked stock.

The results may be explained by the principle difference between a one-stage (carbonate deinked) vs. a two-stage (alkaline peroxide deinked) bleaching processes. In the two-stage process, hydrogen peroxide reacts irreversibly with some of the chromophores or color bodies that can be easily bleached by the hydrosulfite. Subsequent hydrosulfite applications have a reduced amount of easily bleached chromophores with which to react. It is well known that hydro-sulfite bleach response on virgin mechanical pulps is reduced for the same application in two-stage, peroxide-hydrosulfite bleaching. As the composition of the de-inked stock in a newsprint/magazine recycling operation is primarily mechanical pulp, it is not surprising that the response is reduced. The harder-to-bleach chromophores still require the same application of hydrosulfite to drive the bleaching reaction for the harder-to-bleach species. What is unexpected is the response rate of the carbonate deinked stock. In the one-stage process, like in one-stage hydrosulfite bleaching of virgin mechanical pulps, the easily bleached chromophores are still available for reaction, and a higher response is observed. This has not been the response of conventional alkaline-peroxide deinking systems as shown in Table 6. TABLE 6 Deinking Hydrosulfite Brightness Brightness Chemistry Application % ISO Lift Control 0 51.90 ″ 3 56.80 4.90 Carbonate 1 0 50.50 ″ 3 56.50 6.00

The control deinking chemistry was: 0.82% hydrogen peroxide; 0.5% sodium hydroxide; 1.37% sodium silicate; 0.18% DTPA chelant; 0.18% alcohol EO/PO alkoxylate of cloud point 45-50° C. surfactant.

The carbonate 1 deinking chemistry used: 2.5% of a (Na₂CO₃ 6-8 lb/ton solid, Na₂SO₃ 0-2 lb/ton solid, Na₂SiO₃ (40° Bé) 12.5 lb/ton as is); 0.6% fatty acid salt mixture (90%/10% K Stearate/K Behenate); and 0.06% of a C18 alcohol EO/PO alkoxylate surfactant of cloud point 66-68° C.

Bleaching tests were conducted at 5% consistency, for 60 minutes at 55° C., after pH had been adjusted to 5.0-5.2, using stock pulped and floated at the mill (mobile laboratory) with mill water for dilution. The results are shown in Table 7. TABLE 7 Deinking Hydrosulfite Brightness, Brightness Chemistry Application % ISO Lift Control 0 52.80 ″ 10 55.60 2.80 ″ 20 57.30 4.50 Carbonate-2 0 53.00 ″ 10 58.00 5.00 ″ 20 59.00 6.00

The “Control” deinking chemistry used was 1.0% hydrogen peroxide; 1.05% sodium hydroxide; 0.6% sodium silicate as is; 0.2% EDTA; 0.0575% alcohol EO/PO alkoxylate of cloud point 45-50° C. surfactant; 0.0425% tall oil fatty acid blend (TOFA) extender fatty acid.

The “Carbonate 2” deinking chemistry used was: 2.5% of a mixture of Na₂CO₃ 6 lb/ton solid, Na₂SiO₃ (40° Bé) 12.5 lb/ton as is; 0.6% fatty acid salt mixture (90%/10% KStearate/KBehenate), and 0.06% C18 alcohol EO/PO alkoxylate of cloud point 66-68° C. surfactant.

Example 6

To determine if the ink particle size distribution is changed when a sodium carbonate based system is used instead of the conventional sodium hydroxide system, tests were performed using a Spec*Scan 2000/2001 Dirt/Spec Analysis Software by Apogee in conjunction with an Epson 3170 Scanner.

Comparision analysis of test pads made from the same recycle furnish using flotation feed stocks from both the present invention and from a conventional caustic process (control) for a mill showed that (i) during pulping, the carbonate process in combination with the inventive deinking system released more total ink than the conventiaonal sodium hydroxide/-hydrogen peroxide chemistry, and (ii) the ink released by the present invention contains a greater amount of larger ink particles than the conventional caustic process. The carbonate process of this invention also yielded a lower amount of fine ink particles with respect to the total release of ink particles. Ink particles that were <0.04 square millimeter were arbitrarily considered to be adverse fine ink.

Relating these effects to the standard brightness and ERIC measurements of the test pads after flotation made from the same/common flotation feed as described above, a number of conclusions were reached.

Although the deinking system of the present invention using a carbonate pulping regimen releases more total ink, the performance of the flotation stage is not adversely affected as shown by the lower ERIC number of the pads after flotation for the carbonate pulping as compared to a conventional caustic pulping process. (See Table 8, “Spec*Scan Analysis”).

Although the present invention releases more total ink, the ink collector package of fatty acids and high cloud point surfactant is superior to the conventional collectors at removing fine inks (<0.04 square meters) as evidenced by the high brightness and improved bleach response of the stock after flotation. (See Table 8 “Spec Scan Analysis” and Table 9—“Brightness Response Of Deinked Stock”)

Within industry typical ERIC values, the deinked pulp of this invention has a greater/superior brightness gain than that exhibited by the conventional system.

The greater total ink release during pulping of the present invention was unexpected. Conventional wisdom had been that sodium hydroxide was required for effective ink release.

The superior bleach response of the deinked pulp using carbonate pulping and the present ink collector system was also unexpected. Conventional wisdom had been that hydrogen peroxide was required to maintain edge brightness, i.e. unprinted brightness, of the feedstock. The hydrogen peroxide was usually added during pulping.

ERIC values of <250 ppm and preferably <200 ppm after flotation were previously believed required for a final pulp bleach response to be accept-able. i.e., to get a brightness gain of 2 or more points for the addition of 4 or more pounds/ton of sodium hydrosulfite before transferring the deinked pulp to the paper machine. TABLE 8 Spec*Scan Analysis Ink Specs % Ink Specs, % Ink Specs, Post- Post- Total Cumulative Cumulative Area Cumulative Area. Flotation Flotation Chemistry Area, mm² >0.04 mm² 0.04 mm² (Fine Ink) Brightness ERIC, ppm Alkaline Peroxide 116.74 16.3% 83.7% 50.1 243 0.3% Carbonate 169.06 20.8% 79.2% 49.8 226

TABLE 9 Brightness Response Of Deinked Stock Post- Hydro- Pre- bleach sulfite, Bright- Points/lb, Pre-bleach bleach Bright- pounds/ ness Hydro- Chemistry Brightness ERIC # ness ton Gain sulfite Caustic 53.7 261 57.8 4.5 4.1 0.9 Standard, 9/03 Caustic 53.9 217 58.5 3.2 4.6 1.3 Standard, 4/03 Invention 52.1 253 57.2 4.5 5.1 1.1 2/03

The presence of fine ink on deinked stock is difficult to measure without image analysis. It is not included in the ERIC # (below detection limits), only with image analysis can it be tracked. In the bleaching of deinked stock, the presence of fine ink on the fiber reduces the apparent bleaching response obtained for a given bleach application. Virgin fiber mechanical pulp normally has a bleach response to hydrosulfite in the 1.0-1.2 points per pound/ton of hydrosulfite applied. In order to get close to this response in deinked stocks in an alkaline peroxide based system, it was necessary to drive the ERIC# down to <250, more usually to ˜200, to achieve a satisfactory level of fine ink removal. At this ERIC #, level of ERIC, a sufficient amount of fine ink is also removed to allow bleaching response of the deinked stock to approach that of virgin, unbleached mechanical pulp. The deinked stock of this invention exhibits this type of brightness response in the 250-300 ERIC range. 

1. A process for deinking paper being recycled in a carbonate pulping procedure which is performed in the absence of hydroxides and peroxides comprising the addition of (a) at least one non-ionic alkoxylated alcohol surfactant deinking agent having a cloud point of about 55 to 85° C., and (b) at least two different fatty acid ink collectors: (i) at least one C16 to C20 fatty acid and (ii) at least one C22 to C30 fatty acid, wherein the ink collectors are used in a weight ratio of from about 98:2 to about 70:30.
 2. The process of claim 1, wherein the carbonate pulping procedure is performed at a pH of about 7.2 to about 8.5.
 3. The process of claim 1, wherein the carbonate pulping procedure is performed in an alkaline aqueous solution which comprises sodium silicate and sodium carbonate, with no sodium hydroxide.
 4. The process of claim 1, wherein the sodium silicate and sodium carbonate are used in a ratio between about 95 to 5 and about 50 to 50 by weight with respect to each other.
 5. The process of claim 1, wherein the cloud point of the surfactant is about 60 to 70° C.
 6. The process of claim 1, wherein the alkoxylated alcohol surfactant is an ethylene oxide/propylene oxide (EO/PO) alkoxylate of a C14 to C24 alcohol.
 7. The process of claim 6, wherein the alcohol is C18.
 8. The process of claim 1, wherein the saturated fatty acids have iodine values of less than
 10. 9. The process of claim 1, wherein the C16 to C20 fatty acid comprises stearic acid.
 10. The process of claim 9, wherein the stearic acid is added in the form of potassium stearate.
 11. The process of claim 1, wherein the C22 to C28 fatty acid comprises behenic acid.
 12. The process of claim 11, wherein the behenic acid is added in the form of potassium behenate.
 13. The process of claim 1, wherein the weight ratio of the C16 to C20 fatty acid ink collector to the C22 to C30 fatty acid ink collector is about 90:10.
 14. The process of claim 1, wherein the surfactant is added in an amount of about 0.05 to 0.5% by weight based upon the weight of the paper.
 15. The process of claim 1, wherein the fatty acid ink collectors are added in a total amount of about 0.05 to 0.75% by weight based upon the weight of the paper. 